GaN half-bridges on electrical and thermal co-designed ceramic substrates

This work presents an analysis of an electrically and thermally optimized GaN half-bridge module based on ceramic a substrate. An effective thermal and electrical co-design is a decisive factor in achieving high efficiency and power density. In order to utilize the advantages of both GaN for high switching frequencies and ceramic substrates for excellent thermal properties, an electrical and thermal co-designed substrate stack-up for MHz applications is presented. This stack-up features a 40μm thin ceramic layer resulting in a measured power loop inductance of Lloop,VNA=489pH and a ceramic carrier for an electrically isolated and thermally optimized connection to the heat sink. In a 48V to 24V buck converter switching at frequencies of up to 2 MHz, a difference in efficiency of 1% is achieved compared to a electrically enhanced rigid-flex substrate using a 25μm polyimide layer. At a switching frequency of 500kHz, a power density of 1kW/cm3 is achieved with an efficiency of over 95%, accompanied by the possibility of significantly improving the thermal resistance with an all-ceramic stack-up, which enables GaN half-bridges with high frequencies and power densities.